1. Field of the Invention
The present invention relates to an apparatus, such as a lathe, for use in the generation of ophthalmic products from blanks, and, in particular, to a apparatus for use in the generation of visual lenses, such as spectacle lenses and contact lenses, and lap tools for use in the ophthalmic industry. The invention also relates to a method of operating such a apparatus.
2. Discussion of the Related Art
U.S. Pat. No. 4,989,316 to Logan et at. discloses a machine for generating spectacle lenses and laps which may include a toric surface finish. In this particular machine the generation is achieved by means of a milling tool which acts on a rotating work-piece. The relative position of the milling cutter to the work-piece, both linearly and angularly, is controlled by a computer, where the linear position of the milling cutter is controlled along the rotational axis in response to (i) the angular position of the work-piece with respect to a reference plane, and (ii) the displacement of the cutter from the rotational axis.
The drawbacks of the above configuration of generating machine for ophthalmic products are two-fold, and as follows:
1) The finish generated on a lens by a milling cutter is coarse in nature. Consequently, extensive fining and polishing of the surface has to be employed. As will be well appreciated by those in the industry, the fining and polishing employed with visual lenses such as spectacle lenses involves a lap tool which is moved in short stroke motions across the surface being polished. No matter how good a match the surface of the lens is to the surface of the lap, a coarsely generated lens surface will take longer to fine and polish than a more finely produced surface; and
2) Where the angular displacement of the work-piece is used to drive the linear displacement/alignment of the work-piece with respect to the milling cutter, the control of the machine is necessarily time consuming and inherently prone to in-built following error. One of the reasons for this is that the speed of rotation of the work-piece and the distance from the tool to the work-piece rotational axis are independently controlled, requiting the third and final axis to be highly responsive to the variations of first two axes. A consequence of this is that the generator described is reactive and not proactive. Thus, if the independent axes are inaccurate, the third axis is required to be highly reactive to adjust for the misalignment, which might exceed the limitations of the machine.
Additionally, prior art systems have suffered from a problem of disposing of the waste material, or swarf, produced in the cutting operation. Typically, this material is removed from the location of a cutter head by a vacuum operation, other mechanical means, an operator's hand, and/or a combination of these operations. However, the swarf can be in the form of long strands of material (when not employing a milling machine such as disclosed in the Logan et al. patent), particularly when the material being cut is a polycarbonate material, which tend to clog the machinery. Of course, the employment of an operator's hand near a cutter tool creates a safety hazard.
The prior art has aim suffered from a lack of an accurate and fast calibration system. For instance, the prior art requires that the X-axis and the Y-axis movement devices be precisely orthogonal to one another. This requires that the machine be carefully designed, built and aligned to fight tolerances, requiring relatively large expenditures in time, labor and machinery. Also, each time a blank of different dimensions than the previous blank is inserted into a prior art system, the lathe has to be carefully adjusted to accommodate the new blank.
The prior art has also suffered from a lack of a quick, simple and accurate cutter height adjusting mechanism and method of determining the cutter head height alignment.